The present invention relates to a circuit arrangement, in particular for triggering an ignition output stage, having a power switching transistor and at least one switchable freewheeling circuit and/or switchable autonomous auxiliary channel.
When inductive loads are shut down, voltage spikes can occur as a result of energy stored in the inductive load. If what is desired is a minimum-loss switch, for example in the case of a clock-timed current controller in the load circuit, it is known that a freewheeling circuit having the lowest possible internal resistance, to which the load current is switched over upon shutdown of the power switch, represents an appropriate solution.
If, on the other hand, what is desired is rapid dissipation of the inductive energy (for example when switching a solenoid valve), or attainment of a high primary voltage for operation of an ignition transformer, then a freewheeling circuit which may optionally be present must be configured in switchable fashion.
German Patent Application No. 4344126 describes for example, a circuit arrangement having a switchable freewheeling circuit, the latter having a freewheeling diode, a freewheeling switching transistor, and a semiconductor component having a defined breakdown voltage. This circuit arrangement is relatively complex, and is expensive to manufacture.
The circuit arrangement according to present invention has the advantage that it has a simple design and can be obtained, without additional process steps, during the manufacture of the power switching transistor. Because the freewheeling circuit or an autonomous secondary channel is constituted by a triggerable four-layer element, it is possible to create the entire circuit arrangement with a few process steps that can be linked with processing of the power switching transistor. The present invention provides vertical power transistors having autonomous auxiliary channels, whose dielectric strength is comparable to that of the associated power transistor and which can be implemented easily (without additional process steps). In one embodiment of the present invention, provision is made for a thyristor to be monolithically integrated into the power switching transistor, and preferably to be integrated as a lateral component into the edge region of a power switching transistor crystal. As a result, there is only a small additional space requirement for accommodating the thyristor; because of the lateral arrangement of the thyristor in the crystal, a high level of temperature stability can simultaneously be established.